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Full text of "Metallurgy Of Cast Iron"

UTILITY   OK   THK   TEST   BAR,    ETC.                   533
Because the i/s-incli round bar is large enough not to have its carbon severely distorted to make tests erratic or belie the ruling" power of the percentage of iron, etc., in the metal, by the chilling influence of a green sand mould, and also because it is not so small but that strong grades can often, for rough estimates, be used for comparison with weak grades on low-priced testing machines, are reasons why the author used a bar as small as i \ a -inch diameter as one standard for making comparative tests. Having shown in many tests, (page 468) that the i jy-inch round bar will fairly record degrees in the strength of cast iron to fairly agree in a comparative way with the commercial value attached to the strengths of the various mixtures ranging from stove plate up through light machinery, heavy machinery, car wheel, chill roll and gun metal, the author would now refer to two other sizes, if 8-inch and 11 "-inches diameter as being also well fitted, for recognition as standard bars. The two latter sizes of bars are best utilized by founders who may make mixtures containing less than 1.50 in silicon and above .04 in sulphur. For those above 1.75 in silicon and. below ,07 in sulphur in the test bar or casting, the ij/n-inch diameter bar will be found to generally record fair comparisons in degrees of strength.*
it is to be understood that while either size of the above three proposed, standard bars would not err much in recording true degrees in. the strength, deflection, and contraction where com-parisons arc to be made in any one "grade" or in
* While the i js-ineh round bar will answer fairly well for making tfc'iKTul comparisons in all irons having over 1.75 silicon and under .07 sulphur, still the author approves the recommendations found on page 573, which show that test bars should not be smaller than \y* inches in diameter, and cast on end, us such will tfive truer results than the [J4™inch round bar in general practice, especially in making comparison <>i; the widest ranges in grades.temper '' or damp-              ,| |